The present invention relates to a technique for preventing a starting pulse from being supplied to a discharge lamp in a state in which the discharge lamp is not surely connected to a socket and also simplifying a circuit configuration therefor.
Recently, a small-size discharge lamp (metal halide lamp etc.) has received attention as a light source substituting for an incandescent lamp and, for example, as a configuration of a lighting circuit in the case of being applied to a light source of a lamp for vehicle, the lighting circuit comprising a DC power source, a power source part (switching power source circuit), a DC-AC conversion circuit and a starting circuit has been known.
On starting a discharge lamp, a starter transformer is required as a circuit for generating a starting pulse with high voltage, and a primary side circuit including a primary winding of the transformer is provided with a capacitor for accumulating an electric charge and a switch element for discharging this electric charge. Incidentally, as the switch element, a separately excited type configuration for receiving a signal from another circuit to control the conduction timing as a thyristor element and a self-excited type configuration for conducting at the time when a voltage across an element becomes a defined value as typified by a self-breakdown type element such as a spark gap element have been known.
By the way, with regard to selection of any of the two kinds of the switch elements, it is related to a form of a lighting control circuit (ballast circuit) and a starting circuit (starter circuit) of the discharge lamp. For example, when both the circuits are mounted on the same circuit board without a cord and are housed in one case, any of the two kinds of the switch elements may be used, but when both the circuits are arranged at a distant place and are wired by a cord, the self-excited type configuration becomes advantageous. The reason is because in the separately excited type configuration, disturbance noise is superimposed on a control signal for turning on or off the switch element and a malfunction of the switch element is feared. Also, with regard to wiring, in the separately excited type configuration, a signal line is required for electric charge supply of a primary side capacitor and control of a switch element in addition to two power supply lines.
In recent years, miniaturization of starter circuit components has developed and, for example, a form of integrating the starter circuit with the discharge lamp or a form of holding the starter circuit within a valve socket for discharge lamp connection has been used in application to a discharge lamp for vehicle. That is, the starter circuit tends to be arranged immediately near to the discharge lamp and be located at a place distant from the ballast circuit and thus, the self-excited type configuration using the self-breakdown type element is in the mainstream and there is no trouble of a malfunction and also, there is a cost merit in which two wirings of connection between the ballast circuit and the starter circuit will do.
FIG. 7 shows only the main part in a conventional configuration example, and shows a configuration of an output stage of a ballast circuit of a lighting circuit A and a starter circuit.
In a transformer C constructing a starter circuit B, one end of a secondary winding c2 of the transformer is connected to a power supply terminal ta1 and the other end is connected to an output terminal to. Also, in a primary winding c1 of the transformer C, one end of the primary winding is connected to an electric charge supply source D within a ballast circuit and a spark gap element E is connected to the other end side which is connected to the electric charge supply source d through the element. Incidentally, a capacitor F is interposed between connection terminals of a primary side circuit of the transformer C and the electric charge supply source D.
The other terminal ta2 of a pair of power supply terminals ta1, ta2 is connected to an output terminal toxe2x80x2 and connections between the terminal and the output terminal to and a discharge lamp G are made through a connecting member H such as a socket (for example, a base part of the discharge lamp is fitted and coupled to the socket and each the terminal to, toxe2x80x2 is individually connected to each electrode terminal of the discharge lamp G, respectively).
The present circuit is formed into a configuration of a four-terminal connection in the case of electrical connections between the ballast circuit and the starter circuit, but as a circuit in which this is formed into a configuration of a three-terminal connection, a configuration example shown in FIG. 8 is given.
In a lighting circuit Axe2x80x2, one end of a primary winding c1 of a transformer C and one end of a secondary winding c2 are connected to a power supply terminal ta1 and also are connected to one end of a capacitor F. As a result of this, connection terminals of a ballast circuit and a starting circuit B can be reduced by one (incidentally, in the present example, a reference potential of an electric charge supply source D is grounded, but the grounding may be performed anywhere as long as a feeding path to the capacitor F can be formed).
By the way, since a starting pulse supplied to a discharge lamp is a high voltage, it is necessary to take measures against the case of turning on a lighting switch in a state in which the discharge lamp is not connected to a lighting circuit. This is because, for example, a breakdown may be caused when a high voltage is applied to a connection terminal within a valve socket and this state is left for a long time, or an operator may accidentally touch a connection terminal of a socket to trigger an electric shock accident when replacement operations of the discharge lamp are performed with forgetting that there is in a state of turning on the lighting switch.
Hence, there is considered a method constructed so that a feeding path for accumulating an electric charge in a capacitor within a starter circuit is formed when a discharge lamp has been connected using high voltage connection means (a valve socket etc.) and the feeding path is not formed when the discharge lamp has been disconnected from the high voltage connection means.
FIG. 9 and FIG. 10 show a main part of such a configuration example, and both the figures are based on the circuit example of FIG. 8.
Differences between a circuit example I shown in FIG. 9 and the circuit of FIG. 8 in the configuration are as follows.
A valve socket J is interposed between a lighting circuit and a discharge lamp G, and three terminals k1, k2, k3 are provided within the socket J.
Three terminals g1, g2, g3 are provided in a connection part (base part) of the discharge lamp G to the valve socket J, and the terminals g1, g2 of the three terminals are respectively connected to each electrode terminal of the discharge lamp G and the terminal g3 is connected to the terminal g2.
In a state in which the discharge lamp G is connected to the valve socket J, the terminal g1 is connected to the terminal k1 and the terminal k2 is connected to the terminal g2.
With respect to an electric charge supply source D, one end of the electric charge supply source D is connected to a connection point of a spark gap element E and a capacitor F and the other end is connected to the terminal k3.
In a state in which the discharge lamp G is connected to the valve socket J, the terminal k2 is connected to the terminal k3 and both the terminals are connected to a power supply terminal ta2.
Thus, in the present circuit I, when the discharge lamp G is disconnected from the valve socket J and the terminals k2 and k3 become a non-connection state, a feeding path to the capacitor F is not formed, so that generation of a starting pulse is prohibited.
Also, differences between a circuit example L shown in FIG. 10 and the circuit of FIG. 8 in the configuration are as follows.
A valve socket m is interposed between a lighting circuit and a discharge lamp G, and four terminals n1, n2, n3, n4 are provided within the socket M.
Four terminals g1, g2, g3, g4 are provided in a base part connected to the valve socket M of the discharge lamp G, and the terminals g1, g2 of the four terminals are respectively connected to each electrode terminal of the discharge lamp G and the terminal g3 is connected to the terminal g4.
In a state in which the discharge lamp G is connected to the valve socket M, the terminal n1 is connected to the terminal g1 and the terminal n2 is connected to the terminal g2 of the discharge lamp G.
The terminal n4 is connected to a connection point of a capacitor F and a spark gap element E.
The terminal n3 is connected to one end of an electric charge supply source D.
In a state in which the discharge lamp G is connected to the valve socket M, the terminal n3 is connected to the terminal g3 and the terminal n4 is connected to the terminal g4.
Thus, in the present circuit 1, when the discharge lamp G is disconnected from the valve socket M and the terminal n3 and the terminal n4 become a non-connection state, a feeding path to the capacitor F is not formed, so that generation of a starting pulse is prohibited.
However, with respect to the configurations of FIGS. 9 and 10, the following problems remain.
Though it is hard formed into a configuration of a three-terminal connection as the configuration shown in FIG. 8, a portion between a ballast circuit and a starter circuit returns to a four-terminal connection in FIG. 9.
In FIG. 10, it is necessary to increase connection terminals for connecting the discharge lamp G to the valve socket M by one to four, so that a design modification is forcedly made to a socket structure (at present, a three-terminal connection) and also there arise disadvantages in cost or safety.
An object of the invention is to reduce cost and improve safety by decreasing the number of connection wirings among a lighting control circuit, a starting circuit and a discharge lamp in a lighting circuit constructed so that a starting pulse is not generated in a state in which a discharge lamp is not connected to a socket.
In order to solve the problem described above, the invention comprises the following configurations in a discharge lamp lighting circuit comprising a lighting control circuit for performing lighting control of a discharge lamp, a starting circuit for supplying a starting pulse to the discharge lamp, and a socket connected to said discharge lamp in order to supply electric power and the starting pulse to the discharge lamp.
The starting circuit provided within the socket has a transformer, a capacitor connected to a primary winding of said transformer and a self-breakdown type switch element, and a feeding output terminal for performing a feeding from the lighting control circuit to the starting circuit is connected to the capacitor directly or through the primary winding and also an accumulation electric charge of said capacitor is discharged through the primary winding of the transformer by conduction of the self-breakdown type switch element and thereby the starting pulse is generated and said pulse is supplied to the discharge lamp through a secondary winding of the transformer.
First and second terminals of three terminals provided in the socket are respectively connected to each electrode terminal of the discharge lamp and also the second terminal is connected to the secondary winding of the transformer and a third terminal is connected to the capacitor of the starting circuit directly or through the primary winding.
A connection between the lighting control circuit and the starting circuit is made by a cord wire.
With respect to a pair of output terminals of the lighting control circuit, one output terminal is connected to the second terminal through the secondary winding of the transformer and the other output terminal is connected to the first terminal.
It is constructed so that a feeding path to the capacitor is formed through the feeding output terminal to charge said capacitor only when the discharge lamp is connected to the socket and a connection between the first terminal and the third terminal is made.
According to the invention, when the discharge lamp is not connected to the socket in a complete state and a connection between the first and third terminals is not made, the feeding path to the capacitor is not closed in the starting circuit, so that the starting pulse is not supplied to the discharge lamp. Then, a connection can be made by three terminals among the lighting control circuit, the starting circuit and the discharge lamp.